1. Field of the Invention
The present invention relates to a liquid droplet ejection mechanism and an image forming apparatus, and more particularly to a liquid droplet ejection mechanism and an image forming apparatus that can prevent increase in the viscosity of circulated ink and can suppress the amount of ink which is circulated wastefully.
2. Description of the Related Art
International Publication No. WO00/38928 discloses an apparatus which circulates ink in a nozzle section during ink ejection, in order to perform a head cleaning (to remove foreign matter). FIG. 17 is a cross-sectional diagram of a print head 201 disclosed in International Publication No. WO00/38928. The ink which flows out from the first ink tank (not illustrated) flows from a channel 210 into a first column 212 and a second column 213 of a chamber, via an opening section 211. Thereupon, the ink flows out via opening sections 214 and 216 and the ink flow is made to converge by passing along a first ink outlet channel 217 and a second ink outlet channel 218, and is then recovered in a second ink tank (not illustrated). Thereupon, the ink is returned from the second ink tank to the first ink tank and then supplied again to the channel 210, thereby circulating the ink.
Circulating the ink in this way brings about the effect that the chamber is kept clean efficiently and the effect that stagnation of ink in the nozzle sections inside the inkjet head is prevented, so that increase in the viscosity of the ink is prevented.
However, in the invention described in International Publication No. WO00/38928, ink which has exited to the outside of the print head 201 is returned again to the second ink tank and the first ink tank. Here, the ink which has exited to the outside of the inkjet head from the pressure chambers in the head via the nozzles has increased in viscosity due to the evaporation of solvent in the nozzle sections. Therefore, the ink viscosity increases as the ink is circulated, and ejection defects may eventually occur in the nozzles.
In response to this, it would be possible to discard ink which has exited to the outside of the head, rather than returning this ink to the first ink tank, but since the amount of circulated ink is very large, the amount of discarded ink would also become very large, leading to poor efficiency.
Furthermore, it is also possible to add solvent in order to return the ink to its original viscosity, before returning the ink to the first ink tank, but this would require a mechanism for adding the solvent and hence the inkjet recording apparatus becomes very large in size. Moreover, since the amount of solvent to be added varies with the air temperature and humidity, it is not easy to return the ink to its original viscosity.